Green is freedom states, blue is semi-freedom states (how much depends on how strict state laws are), yellow is horrible state, and red is mega horrible state.
That map is kind of misleading for Minnesota, the only legal fireworks here are ones that don't shoot into the air, so basically the more boring ones. Of course people just import them from Wisconsin which is far less restrictive, and still shoot them off everywhere. I actually saw people shooting them off in public parks of all places yesterday to give an idea of how widely ignored the law is.